In their basic form, disposable absorbent articles comprise an absorbent core interposed between a pervious body-contacting element (alternatively referred to as a topsheet or an overwrap) and an impervious protective barrier (alternatively referred to as a backsheet). The absorbent element is, of course, intended to receive and contain the fluids discharged from the body. The body-contacting element is intended to provide comfortable and dry-feeling contact with body surfaces while allowing free passage of fluids therethrough into the absorbent element. The protective barrier is intended to prevent the fluids which are expelled or which escape from the absorbent element from soiling the user's garments.
In addition to the three functional elements mentioned above, disposable absorbent articles are generally provided with means for supporting the device adjacent the user's crotch area, where it can most effectively perform its intended function. Typically, absorbent articles as sanitary napkins are provided with an adhesive attachment means for securing the device to the inner crotch area of the user's undergarments.
Improved fluid interception can occur if the absorbent article is in close contact with the body of the wearer.
While previously known absorbent articles do perform their intended function, each conventional design can be further improved in one or more of absorbency of body fluids, protection of the user's garments from soiling, and/or physical comfort to the user.
With respect to disposable sanitary napkins several attempts have been made in the art to improve body contact with the wearer, and hence absorb fluids upon discharge and thereby minimize soiling, by providing a sanitary napkin having an anatomically shaped configuration, particularly including those that are raised upwardly or humped in their medial portions so as to be near or in contact with the pudendal region when worn.
On female users these sanitary napkins attempt to contact and absorb menses immediately as it leaves the vestibule.
Some articles have also been described in which an anatomically shaped configuration is provided during the wearing time, with the advantage of a better fit to the anatomy.
According to U.S. Pat. No. 3,512,530 a sanitary napkin is described in which a compressed regenerated cellulose sponge layer is combined to a larger fibrous cellulose layer to form a multiple ply absorbent core. The compressed regenerated cellulose sponge layer is positioned over the fibrous layer, and it is typically centered about it; it is intended as the primary absorbent element of the sanitary napkin, while the fibrous layer acts as a secondary or back up absorber.
The sanitary napkin may be therefore very thin prior to use, as compared to other sanitary products having the same absorbent capacity.
Although the compressed regenerated cellulose sponge layer is capable of expanding in Z-direction upon fluid absorption, the structure described is not particularly suitable to provide an effective body contact and might cause discomfort to the user.
When the expansion of the compressed regenerated cellulose sponge layer starts from the point that is first reached by the fluid, it is restrained by the surrounding, still dry regions of the sponge layer at least until they have received liquid by capillary diffusion through the material itself. This may not allow an effective swelling, particularly under absorption of relatively small amounts of fluid, due to the restraining effect of the remaining portions of the material not yet reached by the fluid.
The compressed regenerated cellulose layer may also be rather stiff in its dry state if a higher density, which is particularly useful for a rapid absorption and diffusion of the fluid, is to be provided to overcome this problem.
In European application EP96106724.6, filed on Apr. 29, 1996, an absorbent article is described which comprises a layer for expanding the article into a tridimensional structure while being worn by a user; the expanding layer is activated by body fluids and comprises incisions on at least its body facing surface or its garment facing surface that are arranged in a closed array of intersecting lines.
The incisions provide the expanding layer with the capability of achieving a high degree of swelling even in localized areas and upon activation by small amounts of fluid, and increase the layer flexibility.
Known hydrogel forming materials have been widely used to achieve absorbent layers activated by body fluids; such materials are capable of swelling and could also be used, in principle, to make an expanding absorbent layer. Hydrogel forming absorbent materials, commonly known as superabsorbents, are polymeric materials that can swell and absorb large quantities of liquid, particularly water and water containing fluids, such as body fluids; their use in absorbent articles is well known in the art.
The high absorption capacity of superabsorbents is not, however, combined with rapid absorption and this may adversely affect the performance of absorbent articles incorporating these substances. In fact, superabsorbents may give rise to a phenomenon defined in the prior art as "gel blocking"; when a particle of superabsorbent is in contact with the liquid, its external surface starts to absorb the liquid and swells obstructing the transmission of the liquid into the particle itself; the liquid can penetrate further into the still dry core of the particle only by means of a very slow diffusion mechanism.
Therefore it is desirable to provide an absorbent article with an anatomically shaped configuration for a closer body contact which is achieved during the use upon activation by absorbed body fluids, while it is comfortable for the wearer, easy to produce and to package, and capable of achieving a high degree of swelling even in localized areas and upon activation by small amounts of fluid, combined with the capability of a rapid acquisition and transmission of body fluids, particularly when viscous fluids like menses are to be managed, with an increased flexibility, and with an even better capability of conforming to the user's anatomy.
Hence, it is an object of the present invention to provide an expanding absorbent material that can make full use of its absorbent and expanding capacity without the limitations of the known hydrogel forming materials.